1. Field of the Invention
This invention relates broadly to medical canalicular inserts. More particularly, this invention relates to canalicular plugs which are placed into the punctal opening or the lacrimal duct to prevent lacrimal fluid from flowing through the lacrimal duct.
2. State of the Art
A variety of eye problems are related to an insufficient volume of tears on the surface of the eyes. The most common is keratoconjunctivitis sicca, also known as dry eyes. Contact lens problems are also often provoked by a lack of tear volume. A common cause for the insufficient tear volume is the drainage of tear fluid through the punctal opening of the nasal lacrimal duct and into the nasal passage, thereby removing the fluid from where it is needed at the eye surface. Furthermore, drainage of tear fluid through the nasal lacrimal duct into the nasal passage is believed to be the cause or associated with several additional problems such as post nasal drip, sinusitis, allergies, headaches, and snoring.
A number of methods for closing the punctal opening have been used to prevent drainage of tears through the nasal lacrimal duct, including suturing, laser sealing, and plugging. Plugging with a canalicular plug, such as a punctum plug or a lacrimal plug, is the least severe solution, is relatively inexpensive, and is being performed with increasing frequency.
Referring to prior art FIG. 25, a punctum plug 910 typically is an elongate member having a proximal head 912, a relatively larger distal body 914 for occluding the lacrimal duct 916, and a relatively narrower rigid shaft 918 therebetween. The plug is usually provided with a proximal axial bore 920 for receiving a cylindrical insertion tool. In the punctum plug insertion procedure, an insertion tool is positioned into the bore 920 of the plug, the body of the plug is directed at the punctal opening 922 of the lacrimal duct 916, and force is applied to the insertion tool to move the body 914 of the plug through the punctal opening 922 and into the vertical puncta 924 and lacrimal duct 916. Once the plug is in the vertical puncta and lacrimal duct, the insertion tool is removed. The plug is fully inserted when the head seats against the tissue at the punctal opening and the body seats within the lacrimal duct so as to block the passage of tear fluid and thereby retain tear fluid at the surface of the eye. Similarly, lacrimal plugs which seat entirely within the lacrimal duct (and below the punctal opening) are also known.
It has been found that prior art punctum and lacrimal plugs, while providing some benefit often do not provide satisfactory occlusion of the lacrimal duct. Tear fluid tends to flow through the interstices between the body of the plug and the tissue of the vertical puncta of the nasal lacrimal duct. One proposed prior art solution of this problem has been to provide an enlarged distal body to the plug. However, the larger distal body is difficult to insert through the relatively small punctal opening.
In addition, with prior art canalicular plugs, completely occluding the lacrimal duct can provoke other detrimental effects. For example, when a patient has a plug implanted in his or her lacrimal duct, simple acts such as sneezing or nose blowing can cause a momentary pressure differential to occur about the plug. That is, referring to prior art FIG. 25, the lacrimal duct 916 on the body side of the plug (below body 914) is subject to increased pressure relative to the head side of the plug (above head 914). This pressure differential can result in the plug being forced up and inadvertently dislodged from the puncta. Other activities, such as eye rubbing and ear-popping (e.g., after scuba diving or flying) can similarly cause a pressure differential and result in inadvertent expulsion of the plug from the lacrimal duct.